Indium plating



Patented June 30, 1;;42

Clarence F. Smart,

No Drawing.

1 Claim.

g zest s r I INDIUM PLATI NGA I I a I Pontiac, Mich, assignor to General Motors Corporation, corporation of Delaware Application December 16, 1938, Serial No. 246,064

Detroit, Mich., a

This invention relates to the electro dcposition of indium and has particular reference ess and bath for sition.

The primary object of my invention is to provide a new and improved bath and process for the electro-deposition of indium having certain advantages over baths and processes heretofore proposed for this purpose. Other objects and advantages will become apparent from the detailed description.

The bath of the present invention is one that has exceedingly good throwing power, is one of good eiiiciency, and one that is. easy to operate and control. The allowable ranges of current densities, voltages, etc., for good deposits ar quite broad. The bath is easy to make up in the to a procplating indium by electro-depo- ,first place and is free of the danger of HCN fumes, such as might occur in the making up of a cyanide bath unless the operations are performed under a well ventilated hood, etc. The bath of my invention has little or no tendency to dissolve such metals as iron, nickel. cadmium, silver and copper and thus is not subject to contamination by these metals; in addition, it shows no tendency for the indium to separate on long standing, remaining clear and free from sludge. Deposits plated by the use of my bath and process are smooth, adherent and free from the dark smudge sometimes present in deposits from cyanide baths. The indium may be readily recovered from the bath.

I have discovered that a bath comprising indium, dextrose, an alkali, such as sodium hydroxide or potassium hydroxide, and water has certain advantages in the electro-deposition ofindium over other baths of which I am aware. The indium content may be from about one to six ounces per gallon'of water, dextrose may be approximately half the indium content, but preferably not under about one ounce per gallon, and sodium hydroxide or potassium hydroxide from about six to twelve ounces per gallon. The sodium hydroxide is less expensive than the potassium hydroxide and is, therefore, preferred. A preferred composition is approximately as follows: indium 4 oz. per gallon of water, dextrose 3 oz. per gallon of water, and sodium hydroxide 8 oz. per gallon of water.

The plating bath of my invention operates well at ordinary temperature of 70 it, also at higher temperatures up to 175 F. if desired, over a wide range of voltage and current density. Good, adherent, deposits of indium have been current densities from about 10 to 150 amperes per square foot of cathode area. At lower current densities the deposits are smoother than are those obtained with the higher current densities. Inert anodes, such as carbon, for example, are employed.

The bath may be made bydissolving metallic indium in hydrochloric acid and to this solutionadding a water solution of sodium hydroxide or potassium hydroxidev or the like to which dextrose has been added. The indium is first precipitated as whiteindium hydroxide and then in the presence of excess alkali and dextrose the indium redissolves leaving a clear solution. It is permissible to add the dextrose to either the concentrated sodium hydroxide or potassium hydroxide solution, or to the concentrated solution of indium in acid, and to add either one of these obtained with voltages from about 3 to 10, and

to the other with stirring to dissolve the precipitate which first forms. After mixing the concentrated solutions, water is added in order to obtain the desired solution. The solutions should be cool before mixing, as at boiling temperatures the indium'hydroxide precipitates and does not redissolve. This reaction may be made use of if it is desired to recover the indium from the bath for any reason. For example, it may be desirable to recover the indium from a partially depleted bath with too low indium content for satisfactory current efficiency. By heating the bath to a boiling temperature the indium is completely precipitated as indium hydroxide and may be separated as by filtration, or by settling and decantation. The precipitatemay be redissolved in acid and made into a new plating bath if desired.

In place of hydrochloric acid the indium may be dissolved in other acids such, for example, a"- suiphuric acid or nitric acid. I prefer the hydrochloric acid, however. .as-excess acid can be readily removed from the solution by boiling and because the hydrochloric acid is non-oxidizing to the dextrose. Soluble salts of indium may be used, if available, to dissolve directly in water without acid.

By the use of my bath and process indiummay be plated on metals of various kinds, as desired. My bath is especially desirable in plating bearings or bearing alloys to render the same corrosion resisting. Cadmium alloy bearings and copper-lead bearings may be readily plated with indium to provide a corrosion resisting coating thereon. The plated bearings may be heat treated at about 840 F. to cause the indium to become diffused into the base metal.

While I have described a preferred embodiment of my invention, 'Iam aware that many changes may be-made and numerous details varied without departing from the-principles of my invention and I do not desire to limit the patent granted for my invention except as necessitated by the prior art. Y

I claim? 7 A v A process forthewelectro-deposition otadherent deposits of indium comprising, passing .en electric current through an electrolyte .from'an' inert anode'to a cathodeundera voltage .oiifnom about three toten volts and with acu en tyden -"tion'at a temperature of about 70 E. to 1'25" 'F.

'sity' of about 10 to 5150 amperes .per square-foot oi cathode a-rea;: the electrolytebeing free of at least substantially all I cyanide and consisting of an aqueous'solution"of-the following essen-- 5 tie] con'stituen'tsdn approximately the-amounta:

given pergallon of .water: a compound of-"1n-- dii min -which the indiumcont ent ,iiis about one .tof '?six .o'unces; vdextro'e approximately half the indium content and at least one ounce, and so- 10. :dium hydroxide from'about six to twelve ounces;

said electrolyte being :maintained during opera- CLARENCE I. SMART. 

